Esters and polyesters are commonly used for a wide variety of purposes in the chemical arts. These compounds can be used as coatings, themosetting adhesives, and in many other applications. It is highly desirable to obtain esters and polyesters which can undergo reversible cross-linking reactions without liberating undesirable by-products. It is also desirable to have a method by which long-chain polymeric compounds can be cross-linked so as to further increase their molecular weight and viscosity.